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and after the slabs have solidified samples are cut has two important advantages over a fluorescent and ground and the activity measured. tracer technique previously employed; the tracer A technique in which 198Au is used to trace material can be readily identified and the dispersion sediment movement in the sea has recently been of sediment can be observed directly and correlated adopted in South Africa in the study of harbour with data on winds and tide movements. development. The gold tracer is attached to a sand In the laboratory the 67 KeV K X-ray from a source sample by chemical exchange with silver previously of 795Au has been used in X-ray fluorescence spec- deposited on to the sample by a chemical silvering trometry, but this application is restricted by the process. high cost and comparatively short half-life of the At the test site the radioactive sand is mixed with nuclide. a sediment slurry in a lead shielded pot, which is The transitions of 195Au which generate 98.8 and lowered to the sea bed and emptied by remote control 129 KeV gamma rays exhibit the Mössbauer effect. from the deck. The labelled sand particles are trans- This has been used in studies of the physical and ported by the sea movements and their dispersal chemical structure of metallic platinum and its can then be traced by means of a sensitive gamma alloys, of intermetallic compounds and of oxides and detector towed across the sea bed. This technique halides.

Gold Alloy Spark Plug Electrodes EASIER STARTING AND LONGER LIFE To perform its function efficiently a spark plug must plugs with a smaller diameter insulator tip, allowing maintain a gap spacing that will satisfy engine operation greater clearance between the insulator and the shell over the full range of output from idling to full throttle, at the firing end. This results in better scavenging of achieve this with minimum fuel consumption, and fuel deposits and, as a consequence, better protection resist the effects of both electrical erosion and chemical from fouling. Similarly the marked decrease in gap attack from the products of combustion. erosion observed with these plugs is attributable to the A very great deal of research has gone into the design much greater resistance of the gold alloy to the atmo- and development of the spark plug to meet modern sphere in the combustion chamber by comparison conditions of motoring. One recent development, by with the more conventional electrode materials. Champion Spark Plug of Toledo, Ohio, is the intro- duction of a range of plugs with centre electrodes tipped with gold alloy wire. These spark plugs, although some- what more expensive, have been enthusiastically adopted in such applications as snowmobiles and motorcycles where fast and sure starting is required even in sub-zero weather conditions. The use of the gold alloy electrode — a 60 per cent gold 40 per cent palladium alloy — offers a number of advantages in engine performance, including easier starting and less gap erosion. Easier starting results from reduced voltage required to fire the plug. In addition, since the small size of the electrode means that more spark is exposed to the fuel charge than with standard electrodes, the gap size can be reduced, which again lowers the voltage demand on the ignition system. The outstanding resistance to corrosion of the gold- palladium alloy has made it possible to design these

The centre electrode of this Champion spark plug in a gold- palladium alloy is specifically designed to provide ease of starting even in extremely cold weather conditions, while the high resistance to corrosion of the gold alloy ensures a longer service life than can be expected with plugs fitted with conventional electrodes

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